The present invention relates to a traction machine of a traction type elevator.
When a car of elevator is stopped, the traction machine generally is so controlled that the car decelerates along a given deceleration curve. In the case of high speed elevator system, when the car travels on the terminal portion of a hoistway, the given deceleration curve and its corresponding actual speed of the car are compared and if the car actual speed is higher than the given deceleration, the traction machine is braked. Alternately, when the car passes the given portion of the terminal of the hoistway at a higher speed than the given speed, the traction machine is braked through a speed governor. In this manner, when the car travels abnormally on the terminal portion of the hoistway, the car is decelerated to prevent an accident at the terminal portion. In this case, the car is subjected to a larger deceleration than that when the car normally stops. The traction type elevator is driven by friction between the traction sheave and the main rope. For this, when the traction machine, i.e. the traction sheave, is braked in order to correct the abnormal travel, particularly when the car travels down with the maximum load, there is a high possibility that there will occur a slip of the main rope. Therefore, it can possibly fail to obtain a desired deceleration operation, resulting in occurence of an accident at the terminal of the hoistway.
One of the ways to improve friction between the traction sheave and the main rope is to increase the winding angle of the main rope. However, this is impracticable since there are many restrictions of disposition of elevator system. Another way to improve the friction is to change the main rope groove shape of the traction sheave. According to this method, the surface pressure of the groove is increased to further its wear, resulting in shortening the elevator lifetime. Still another way is to press the main rope out the groove by separately provided roller or the like. This also is followed by increase of the surface pressure and the lifetime of the elevator is shortened. Yet another way is to impregnate the main rope with a friction increasing material such as VANOL oil, asphalt rope grease, or the like. This considerably reduces the lifetime for bent fatigue.